Belgium and the Netherlands are frantically trying to stop the spread of oil leaking from a collision Tuesday morning between a freighter and a tanker in the North Sea before the slick sullies a coastal nature reserve.

The Flinterstar freighter was carrying 125 tonnes of diesel and 427 tonnes of fuel oil when it collided with the Al Oraiq tanker eight kilometres (five miles) off the Belgian coast.

According to the Belga news agency, an unspecified amount of oil had already leaked from the ship and was being vacuumed up.

Belgian and Dutch authorities were attempting to build a protective sand bank around the Zwin nature reserve, which straddles their common border, officials said.

The governor of the West Flanders region in Belgium, Carl Decaluwe, was quoted by the news agency as saying that the measures were preventative.

"Calculations show that it is possible that oil reaches the Zwin," West Flanders authorities said in a Facebook post.

Both boats were damaged in the collision, but the 315-metre (1,000-foot) long tanker was able to make it to the Belgian port of Zeebrugge.

The 130-metre (426-foot)long Flinterstar partially sank in a sand bank. All 12 crew members were rescued.